The serpin superfamily is a large group of medium-size proteins (approximately 45 60kDa) that have a common three-dimensional fold that represents a metastable conformation of the protein. Despite the common tertiary fold, inhibition of serine or cysteine proteinases, blood transport of thyroid hormones, blood generation of the vasoactive hormone angiotensin, neurite-outgrowth-promoting-ability, regulation of tumor invasion, involvement in cellular differentiation and regulation of apoptosis. The long term goal of this program project is to understand the metastable folding pathway and consequences of the metastable serpin fold both for normal and pathological function, and in conferring the particular properties of a given serpin, whether the (anti-thrombin, alpha1-proteinase inhibitor, and crmA), (ii) is able to undergo conformational change but without the ability to inhibit proteinase (thyroxine binding globulin) or (iii) acts neither as an inhibitor nor appears to undergo the serpin conformational change (angiotensin). The present proposal represents a concerted attach on some of the most important outstanding questions on serpin structure and function. The program comprises four projects that address different aspects of this goal. Studies include those on the structure of the nature of the inhibition mechanism of both serine and cysteine proteinases and how serpins are able to kinetically trap complexes with proteinase (Project 2, Steven Olson, P.I.), why the serpin fold should still be needed for the non- inhibitory serpins angiotensinogen and thyroxine binding globulin (Project 3, Phillip Patston, P.I.), and the x-ray structures of serpins and their complexes with proteinases and specific ligands (Project 4, Karl Volz, P.I.). There are three cores consisting of an administrative core, a molecular biology and cell culture core, and a protein expression and purification core. All three cores will be used by all four projects. The project represents an inter-departmental and inter-college collaboration, involving investigators in four departments and two colleges of the University of Illinois at Chicago as well as a group of internationally- recognized collaborating investigators.